The regulation of bacterial growth is mediated through mechanisms which adjust the synthesis of RNA to the potential of the environment to support growth. For rapidly growing bacteria we have shown that this control involves primarily two variables: the instantaneous rate of synthesis of all RNA species, and the fraction of this synthesis given to the formation of the ribosomal and transfer RNA species. To investigate these controls, three projects are proposed: a. Although there exists extensive studies of the control of ribosomal RNA synthesis as a function of growth conditions, much less is known concerning messenger synthesis. Measurements of the rate of messenger synthesis in Escherichia coli similar to those already published will be carried out under various physiological conditions as well as in mutant strains, defective in protein and RNA synthesis, with the objective of characterizing how the total rate of RNA synthesis is limited. b. In vitro studies on the control over the synthesis of the stable RNA species will be carried out using a system we have developed which accurately transcribe and processes a set of transfer RNA's encoded by the bacteriophage T4 genome. This system will be further characterized and factors potentially influencing the transcription of the stable genes evaluated. c. The 5'-terminal nucleoside triphosphates of the nascent RNA of E. coli reflect the first inserted nucleotide on the initiation of RNA synthesis. Measurements are proposed of the synthesis and destruction of these groups as the RNA's bearing them enter their various functions.